The free aquous phase was obtained from individual samples of dental plaque and the plaque matrix was then eluted with a chaotropic buffet in an attempt to remove bound protein. The fluid and the chaotropic phases were assayed for secretory immunoglobulin A (SIgA), IgG, IgM, the third component of complement (C'3), lysozyme, lactoperoxidase and lactoferrin. The prsence of these specific and non-specific immune factors in the free and bound phases suggest they are impor3tant in host defense at the plaque-enamel interface. Analyses by S.D.S. PAGE and immunoplotting revealed that many of the immune protens were degraded into small molecular weight fragments.